The production of hydrogen peroxide by the anthraquinone process is well known. In such processes, an alkylated anthraquinone is hydrogenated in a solvent in the presence of a catalyst to the corresponding anthrahydroquinone which, after separation of the catalyst, is oxidized by means of oxygen to produce hydrogen peroxide. The anthraquinone is regenerated during the oxidation and is recycled to the hydrogenation stage after first removing the product hydrogen peroxide, for example, by extraction with water. In such processes, one mol of hydrogen peroxide is obtained for each mol of the anthrahydroquinone present in solution. It is therefore important that the starting anthraquinone and the corresponding anthrahydroquinone be highly soluble in the solvent or solvents that are employed.
The solvents used in the anthraquinone process have most advantageously been two component systems in which one solvent, usually a hydrocarbon type, is present primarily to dissolve the quinone and the other, a polar solvent, is present to dissolve the hydroquinone. Since polar solvents tend to be relatively soluble in water, contamination of the aqueous hydrogen peroxide extract may become a problem if the polar solvent is not used sparingly. Nevertheless, sufficient polar solvent must be used to permit a high concentration of the hydroquinone to be present in the organic phase. The maintenance of a proper balance between these two criticalities is essential in peroxide manufacture.
German Offenlegungsschrift 2,065,155 published on Nov. 2, 1972 discloses the use of N,N-diethyl-N',N'-dibutyl urea as a hydroquinone and quinone solvent and German Offenlegungsschrift 2,018,686 discloses the use of tetraethylurea in the production of hydrogen peroxide by an anthraquinone process.